1. Field of the Invention
The present invention relates to a satellite broadcast receiver apparatus, more particularly, to a satellite broadcast receiver apparatus intended to reduce power consumption.
2. Description of the Background Art
Now, two broadcasting satellites having a downlink signal frequency band corresponding to the BSS (Broadcasting Satellite Service) frequency band of 12.2–12.7 GHz are launched in the sky above North America in the proximity of 110° and 119° west longitude. There is also a communication satellite having a downlink signal frequency band corresponding to the FSS (Fixed Satellite Service) frequency band of 11.7–12.2 GHz launched in the proximity of 91° west longitude.
In the BSS frequency band, signals through two types of circular polarization, i.e., left-handed polarized wave and right-handed polarized wave, are employed as the transmission signals from the satellite. In the FSS frequency band, signals through two types of linear polarization, i.e. horizontal polarization and vertical polarization, are employed as the transmission signals from the satellite.
In the previous era where there were few broadcasting satellites, reception of single signals from one satellite through one satellite broadcast receiver apparatus was only required. In accordance with the recent increase of broadcasting satellites, there is the growing need for a device that can receive a plurality of signals from one or more satellites through one satellite broadcast receiver apparatus.
A configuration of a conventional satellite broadcast receiver apparatus that can receive a plurality of signals (for example, horizontal polarization and vertical polarization) from a satellite through one receiving antenna is disclosed in, Japanese Patent Laying-Open No. 2000-252741, for example.
FIG. 8 is a block diagram of a configuration of a conventional satellite broadcast receiver apparatus 103 that can receive a plurality of signals from one or more satellites. FIG. 8 exemplifies a configuration of a conventional satellite broadcast receiver apparatus that can receive two types of signals from two satellites.
Referring to FIG. 8, satellite broadcast receiver apparatus 103 includes receiving terminals 10a, 10b, 10c and 10d receiving left-handed and right-handed polarized wave signals corresponding to two types of circularly polarized wave signals in the BSS frequency band of 12.2–12.7 GHz. Receiving terminals 10a, 10b, 10c and 10d are provided in one antenna (not shown).
Receiving terminals 10a and 10b receive a left-handed polarized wave signal L1 and a right-handed polarized wave signal R1 from a satellite at west longitude 119°, respectively. Receiving terminals 10c and 10d receive a right-handed polarized wave signal R2 and left-handed polarized wave signal L2 from a satellite at west longitude 110°, respectively. In the present specification, left-handed polarized wave signal L1, right-handed polarized wave signal R1, right-handed polarized wave signal R2 and left-handed polarized wave signal L2 are also simply referred to as L1, R1, R2 and L2, respectively.
Satellite broadcast receiver apparatus 103 further includes a low noise amplifier (LNA) 11 that is an amplifier of low noise, bandpass filters (BPF) 12a, 12b, 12c and 12d passing through only signals having a predetermined frequency, a mixer 13 providing signal outputs of the intermediate frequency band of 950 MHz–1450 MHz, and a local oscillation circuit 40 providing a signal output of a predetermined frequency.
LNA 11 includes LNA 11a, LNA 11b, LNA 11c and LNA 11d. LNA 11a and LNA 11b amplify L1 and R1, respectively. LNA 11c and LNA 11d amplify R2 and L2, respectively.
BPFs 12a and 12b remove the image frequency (for example, frequency in the vicinity of 10 GHz) corresponding to the unrequired frequency band from L1 and R1 amplified by LNA 11a and LNA 11b, respectively, to output the image frequency removed signals. Similarly, BPFs 12c and 12d remove the image frequency from R2 and L2 amplified by LNA 11c and LNA 11d, respectively, to output the image frequency removed signals.
Mixer 13 includes a mixer 13a, a mixer 13b, a mixer 13c and a mixer 13d. Mixers 13a and 13b respectively multiply L1 and R1 having the image frequency removed by a signal of a predetermined frequency (for example, 11.25 GHz) output from a local oscillation circuit 40 to output signals L1′ and R1′, respectively, having an intermediate frequency of 950 MHz–1450 MHz.
Mixers 13c and 13d respectively multiply R2 and L2 having the image frequency removed by a signal of a predetermined frequency output from local oscillation circuit 40 to output signals R2′ and L2′, respectively, having an intermediate frequency of 950 MHz–1450 MHz.
In other words, each of signals L1, R1, R2 and L2 has the frequency converted by LNA 11a, LNA 11b, LNA 11c and LNA 11d, respectively, BPF 12a, BPF 12b, BPF 12c and BPF 12d, respectively, and mixers 13a, 13b, 13c, and 13d, respectively, to be provided as signals L1′, R1′, R2′ and L2′, respectively.
Satellite broadcast receiver apparatus 103 further includes a switch circuit 15 switching a plurality of signals for output, intermediate frequency (IF) amplifiers 16a and 16b amplifying the signal output from switch circuit 15, capacitors 17a and 17b cutting off the direct current component of an input signal, and input/output terminals 21a and 21b. 
Satellite broadcast receiver apparatus 103 further includes receivers 22a and 22b connected to input/output terminals 21a and 21b, respectively, diodes 20a and 20b, a control microcomputer 18, a voltage conversion circuit 19 converting the voltage of an input signal to a desired voltage level, and a power supply control circuit 14. Receivers 22a and 22b are a television, a video, and the like incorporating a satellite broadcasting tuner. Control microcomputer 18 internally includes a resistor to lower the voltage of a signal from a receiver to a desired voltage level.
Switch circuit 15 can output two of the input signals L1′, R1′, R2′ and L2′ to IF amplifiers 16a and 16b, respectively. Switch circuit 15 can also output one of input signals L1′, R1′, R2′ and L2′ to one of IF amplifiers 16a and 16b. Furthermore, switch circuit 15 can output one of input signals L1′, R1′, R2′ and L2′ to both IF amplifiers 16a and 16b. The signal output from switch circuit 15 is provided to IF amplifier 16a or 16b. The signal applied to IF amplifiers 16a and 16b is passed through capacitors 17a and 17b, respectively, to be provided to input/output terminals 21a and 21b, respectively.
The control signal output from receivers 22a and 22b to select a desired signal among a plurality of signals from one or more satellites is applied to input/output terminals 21a and 21b, as well as to control microcomputer 18 and voltage conversion circuit 19 via diodes 20a and 20b, respectively. Control microcomputer 18 outputs to switch circuit 15 a select signal SWC1 upon receiving a control signal from receiver 22a, and a select signal SWC2 upon receiving a control signal from receiver 22b. Select signals SWC1 and SWC2 are signals to select a desired signal among signals L1′, R1′, R2′ and L2′.
The voltage supplied from a receiver is generally higher than the voltage used in circuitry in a satellite broadcast receiver apparatus. Therefore, voltage conversion circuit 19 removes the alternating current component of the output signal having a predetermined voltage from at least one of receivers 22a and 22b for reduction to a predetermined voltage level. This voltage is supplied to power supply control circuit 14.
Power supply control circuit 14 supplies voltage to circuitry required for operation of satellite broadcast receiver apparatus 103 when at least one of receivers 22a and 22b is connected to input/output terminal 21a or 21b. Specifically, satellite broadcast receiver apparatus 103 attains an inactive state when receivers 22a and 22b are not connected to any of input/output terminals 21a and 21b. By way of illustration, power supply control circuit 14 of satellite broadcast receiver apparatus 103 is shown so as to supply voltage only to LNA 11 and mixer 13. In practice, power supply control circuit 14 also supplies voltage to control microcomputer 18, IF amplifiers 16a and 16b, and local oscillation circuit 40.
Control microcomputer 18 receives a control signal from receiver 22a or 22b to transmit select signal SWC1 or SWC2 to switch circuit 15. Switch circuit 15 responds to select signal SWC1 or SWC2 to provide one of input signals L1′, R1′, R2′ and L2′ to IF amplifier 16a or 16b. 
Receiver 22a or 22b can receive a desired signal from two types of signals from two satellites, i.e. four types of signals, by sending a control signal to control microcomputer 18.
The above-described conventional satellite broadcast receiver apparatus that can receive a plurality of signals from one or more satellites is rendered active by a voltage supplied from a receiver connected to the input/output terminal and has the voltage supplied to all LNAs and mixers even if only one of a plurality of types of signals from one or more satellites is selected. Therefore, the LNA and mixer not required for the frequency conversion operation were constantly operated. In other words, the conventional satellite broadcast receiver apparatus consumes power that was not required.
Useless power consumption leads to heat generation of the satellite broadcast receiver apparatus per se, whereby the electronic components of internal circuitry will be used under high temperature. This will reduce the lifetime of the electronic components. Heat generation will adversely affect the lifetime of the product of the satellite broadcast receiver apparatus.
Temperature increase within the satellite broadcast receiver apparatus will also cause the frequency of the internal local oscillation circuit and the like to vary greatly. The probability of erroneous operation of the satellite broadcast receiver apparatus will become higher.